Parallel Query Tuning - Expert Oracle RAC Performance Diagnostics and Tuning - page 255

inst_id status calibration_time
------- ------------- -------------------------
2 IN PROGRESS 02-APR-10 09.54.07.105 PM
1 IN PROGRESS 02-APR-10 09.54.07.105 PM
/

When the calibration is complete, calibration status changes to READY :

inst_id status calibration_time
------- ------------- --------------------------
2 READY 02-APR-10 10.14.12.846 PM
1 READY 02-APR-10 10.14.12.846 PM

Once I/O calibration is complete, the calibration statistics can be viewed using the following:

SELECT MAX_IOPS,
MAX_MBPS,
MAX_PMBPS,
LATENCY,
NUM_PHYSICAL_DISKS
FROM DBA_RSRC_IO_CALIBRATE;

MAX_IOPS MAX_MBPS MAX_PMBPS LATENCY NUM_PHYSICAL_DISKS
---------- ---------- ---------- ---------- ------------------
10735 1804 60 8 8

CPU
With this value set for the PARALLEL_DEGREE_LIMIT parameter, the maximum DOP is limited by the number of
CPUs in the system. The formula used to compute the DOP in this situation is PARALLEL_THREADS_PER_CPU *
CPU_COUNT * ( number of active instances ) . If database services have been configured, the number of active
instances is further confined by the number of preferred instances where the database service is active. This again
depends on the type of database management method selected, that is, admin managed or policy managed, which
we discuss later in this section.
Figure 8-7 illustrates the parallel execution process on a RAC environment. The QC process is on SSKY2 because
SSKY2 is the query initiator. Notice that there are several parallel query slave (QP) processes spread across several
instances in the cluster. This is because the query used the SALES service as its connect descriptor to execute this query.
Parallel slaves are confined to the instances where the service is currently enabled, in other words, it has a service
affinity when executing slaves. The number of nodes that can participate in the parallel execution depends on the DOP.

SALES

Node 1 Node 2 Node 3 Node 4 Node 5 Node 6

QC QP

QP QP

SSKY2 SSKY3 SSKY4 SSKY6

SSKY1 SSKY5

QP

Figure 8-7. Parallel servers ( UNIFORM service) in a RAC environment